1. Field of the Invention
The invention relates to new aminoamide acrylate polymer compositions useful as hot melt adhesives which are thermally curable. In particular it relates to aminoamide acrylate polymer compositions which perform as hot melt adhesives which are subsequently curable. It also relates to the cured polymers of the invention, and to the process of manufacture of these polymers, both cured and uncured.
2. Brief Description of the Prior Art
Polyamides are a well known class of thermoplastic polymer. Most polyamides offer no practical means by which they can be cured to thermoset polymers. A known subclass of polyamides are the aminoamide polymers which have free (i.e. non-acylated) amino groups. Certain of these are useful hot melt adhesives, but if they are used in a non-crosslinked thermoplastic mode, they are subject to cold flow, remelting, solvent attack and other modes of deterioration. It is known to crosslink aminoamides, in fact they are often used themselves as crosslinking agents for epoxy resins, but such crosslinking is generally accomplished by means of a "two package" system, the aminoamide resin being one package, and a coreactive resin, typically an epoxy resin, being the other package. Such "two package" systems are commercially used, but have the shortcomings of requiring two containers, measuring and mixing at the point of use, limited working time after the mixing, and they generally require substantial time and/or heating to effect partial cure, to give green strength. Even further time and/or heating is required for complete cure.
It has been known further to blend acrylate polymers into certain polyamides for improved properties such as for hot melt adhesive uses, as in U.S. Pat. Nos. 4,132,690 (E. Ernstman et al.) and 4,374,231 (Doucet), for molding resin uses as in U.S. Pat. No. 4,247,665 (Daniels et al.), and for pressure-sensitive adhesive uses, as in U.S. Pat. No. 4,696,965 (Rasmussen). However, the acrylate polymers in all of these instances had the acrylate group already polymerized and thus rendered nonfunctional. Thus, such blends were in most cases not chemically linked by covalent bonds and in all cases were not capable of being post cured to render them thermoset (infusible). Grafts and copolymers of polyamides and acrylates, suitable for adhesive uses, are taught in U.S. Pat. Nos. 4,247,665 (Daniels et al.) and 4,378,448 (Park et al.) but these also had the acrylate group used up in the grafting or copolymerization and so were not thermally curable.
Curable adhesives have been made using acrylate groups as the curing means as in U.S. Pat. Nos. 4,153,776 and 4,430,479 (Merton et al.) but these did not utilize aminoamides.
Our invention provides an improvement over the prior art in that it makes possible a one package system, with good storage properties, with good hot melt adhesive properties, and with the important added ability to be cured thermally. Thus, it can provide hot melt adhesives, varnishes, lacquers, inks and encapsulants which have good initial (green) strength properties, but, in addition, are rapidly curable to a state where they have improved adhesive strength and gain resistance to cold flow, remelting (or softening with heat), blocking, solvent attack, and moisture damage. These characteristics are especially valuable in hot melt adhesives which must perform under challenging conditions of temperature, humidity, and mechanical stress.